在固液混合相区物质剪切模量的讨论

 从实验和理论两个方面对处于固液相变平衡条件下物质在固液混合相区的剪切模量进行了讨论,认为物质的剪切模量在开始熔化时并不等于零。采用逾渗理论对物质在固液混合相区的固相连通性进行了计算,得到物质整体剪切模量消失的临界熔化质量分数为0.687左右。所给出的物质的熔化失稳因子F(p)能够定性的描述处于固液相变平衡条件下物质固液混合相区内相关物理参量的变化。     

Influence of oriented β‐lamellae on deformation and pore formation in β‐nucleated polypropylene

Four β‐nucleated polypropylene samples with increasing die draw ratio (DDR) were prepared to modify lamellae arrangement. The DSC, SEM, and 2D‐XRD results show that all four cast films had similar crystallinity, high contents of β‐crystal but lowering stability of β‐lamellae with ascending DDR. Meanwhile, the anisotropy of β‐lamellae distribution strengthens gently and the stacked lamellae structure perpendicular to the machine direction (MD) predominates dramatically. Tensile testing at 25 °C and 90 °C were conducted along MD and transverse direction (TD), respectively. The markedly expanding difference of deformation indicates the anisotropy highlighted significantly. Additionally, when the samples stretched along MD, a more homogeneous deformation occurs with ascending anisotropy, which is completely opposite to the β‐lamellae stability. But samples deformed more heterogeneous when stretched along TD. The characterization of morphological evolutions during stretching shows that the stacked lamellae debonds uniformly and abundant microvoids formed when the sample stretched along MD with higher anisotropy, resulting in evenly dispersion of stress, consequently making a more uniform distribution of defects and a better isotropic deformation. Moreover, the microfibrils and defects distributed uniformly within higher orientation sample after longitudinal stretching stretched along MD, leading to the dramatic improvement of pore size distribution of the membrane after biaxial stretching. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1745–1759     

The Constrained-degree percolation model

In the Constrained-degree percolation model on a graph $(\mathbb{V},\mathbb{E})$ there are a sequence, ${\left(U_e\right)}_{e\in \mathbb{E}}$, of i.i.d. random variables with distribution $U[0,1]$ and a positive integer $k$. Each bond $e$ tries to open at time $U_e$, it succeeds if both its end-vertices would have degrees at most $k-1$. We prove a phase transition theorem for this model on the square lattice ${\mathbb{L}}^2$, as well as on the d-ary regular tree. We also prove that on the square lattice the infinite cluster is unique in the supercritical phase.     

Characteristics of phase transitions via intervention in random networks

We present a percolation process in which the classical Erdo¨s–Re′nyi(ER) random evolutionary network is intervened by the product rule(PR) from some moment t0. The parameter t0is continuously tunable over the real interval [0, 1].This model becomes the random network under the Achlioptas process at t0= 0 and the ER network at t0= 1. For the percolation process at t0≤ 1, we introduce a relatively slow-growing point, after which the largest cluster begins growing faster than that in the ER model. A weakly discontinuous transition is generated in the percolation process at t0≤ 0.5.We take the relatively slow-growing point as the lower pseudotransition point and the maximum gap point of the order parameter as the upper pseudotransition point. The critical point can be approximately predicted by each fitting function of the two points about t0. This contributes to understanding the rapid mergence of the large clusters at the critical point.The numerical simulations indicate that the lower pseudotransition point and the upper pseudotransition point are equal in the thermodynamic limit. When t0> 0.5, the percolation processes generate a continuous transition. The scaling analyses of several quantities are presented, including the relatively slow-growing point, the duration of the relatively slow-growing process, as well as the relatively maximum strength between the percolation percolation at t0< 1 and the ER network about different t0. The presented mechanism can be viewed as a two-stage percolation process that has many potential applications in the growth processes of real networks.     

Unprecedented Role of Hydronaphthoquinone Tautomers in Biosynthesis

Quinones and hydroquinones are among the most common cellular cofactors, redox mediators, and natural products. Here, we report on the reduction of 2‐hydroxynaphthoquinones to the stable 1,4‐diketo tautomeric form of hydronaphthoquinones and their further reduction by fungal tetrahydroxynaphthalene reductase. The very high diastereomeric and enantiomeric excess, together with the high yield of cis‐3,4‐dihydroxy‐1‐tetralone, exclude an intermediary hydronaphthoquinone. Labeling experiments with NADPH and NADPD corroborated the formation of an unexpected 1,4‐diketo tautomeric form of 2‐hydroxyhydronaphthoquinone as a stable intermediate. Similar 1,4‐diketo tautomers of hydronaphthoquinones were established as products of the NADPH‐dependent enzymatic reduction of other 1,4‐naphthoquinones, and as substrates for different members of the superfamily of short‐chain dehydrogenases. We propose an essential role of hydroquinone diketo tautomers in biosynthesis and detoxification processes.     

Aspect ratio effects of multi‐walled carbon nanotubes on electrical,mechanical, and thermal properties of polycarbonate/MWCNT composites

Two multi‐walled carbon nanotubes (MWCNTs) having relatively high aspect ratios of 313 and 474 with approximately the same diameter were melt mixed with polycarbonate (PC) in a twin‐screw conical micro compounder. The effects of aspect ratio on the electrical, mechanical, and thermal properties of the PC/MWCNT composites were investigated. Electrical conductivities and storage moduli of the filled samples are found to be independent of the starting aspect ratio for these high aspect ratio tubes; although the conductivities and storage moduli are still significantly higher than values of composites made with nanotubes having more commercially common aspect ratios of ～100. Transmission electron microscopy results suggest that melt‐mixing reduces these longer nanotubes to the same length, but still approximately two times longer than the length of commercially common aspect ratio tubes after melt‐mixing. Molecular weight measurements show that during melt‐mixing the longer nanotubes significantly degrade the molecular weight of the polymer as compared to very similar nanotubes with aspect ratio ～100. Because of the molecular weight reduction glass transition temperatures predictably show a large decrease with increasing nanotube concentration. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 73–83     

《塑料制品与模具设计》教学改革

《塑料制品与模具设计》课程是高分子材料与工程专业的一门专业课,该门课程具有多学科交叉、综合性和实践性强的特点,与实际生产生活联系紧密。本着培养应用型人才的目标,在教学过程中不断地进行教学改革探索,从理论教学和实践教学入手,注重提高学生的学习积极性和实践能力。培养学生初具模具设计能力,模具课程的改革有所成效。让模具课程改革的成果吸引更多的学生,从而更有力地推动课程的改革,更好地为培养应用型人才服务。     

Relationship between morphology and structure of shape‐controlled CeO2 nanocrystals synthesized by microwave‐assisted hydrothermal method

The influence of synthesis conditions on morphology and structure of CeO₂ nanocrystals prepared by microwave‐assisted hydrothermal method were studied by XRD, TEM, Raman spectroscopy and photoluminescence measurements. Decisive effect of the OH^‐/Ce³⁺ molar ratio in the reaction mixture on the size and shape of CeO₂ nanocrystals was established and explained. Rise of the concentration of OH^‐ groups at the surface of growing CeO₂ nanocrystals promotes shape transformation from irregular (spheroidal) to cube and enables oriented attachment mode of particle growth. I was found that the unit cell parameter and intensity of Ce³⁺ defect related band in the luminescence and Raman spectra in ceria nanoparticles increase as follows: irregular shape nanocrystals < large cube < small primary cube shape particles. The reason is growing contribution of total subsurface volume under {100} faces, exposed by ceria nanocubes, where enhanced concentration of Ce³⁺ and oxygen vacancies occur.     

The critical probability for confetti percolation equals 1/2

In the confetti percolation model, or two‐coloured dead leaves model, radius one disks arrive on the plane according to a space‐time Poisson process. Each disk is coloured black with probability p and white with probability . In this paper we show that the critical probability for confetti percolation equals 1/2. That is, if p > 1/2 then a.s. there is an unbounded curve in the plane all of whose points are black; while if then a.s. all connected components of the set of black points are bounded. This answers a question of Benjamini and Schramm [1]. The proof builds on earlier work by Hirsch [7] and makes use of an adaptation of a sharp thresholds result of Bourgain. © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 50, 679–697, 2017     

Enlargement of subgraphs of infinite graphs by Bernoulli percolation

We consider changes in properties of a subgraph of an infinite graph resulting from the addition of open edges of Bernoulli percolation on the infinite graph to the subgraph. We give the triplet of an infinite graph, one of its subgraphs, and a property of the subgraphs. Then, in a manner similar to the way Hammersley’s critical probability is defined, we can define two values associated with the triplet. We regard the two values as certain critical probabilities, and compare them with Hammersley’s critical probability. In this paper, we focus on the following cases of a graph property: being a transient subgraph, having finitely many cut points or no cut points, being a recurrent subset, or being connected. Our results depend heavily on the choice of the triplet.Most results of this paper are announced in Okamura (2016) [24] without proofs. This paper gives full details of them.